1. Field of the Invention
This invention relates to the method for the manufacture of a continuous sheet of flat glass by supporting molten glass on a pool of molten metal while cooling and forming the glass. More particularly, this invention relates to a method for selectively controlling the temperature of the glass while the glass is supported for forming prior to removal from the supporting pool of molten metal to minimize relative differential flow of glass within the advancing glass.
2. Description of the Prior Art
Molten glass may be delivered onto molten metal and formed into a continuous sheet or ribbon of flat glass according to the teachings of Heal, U.S. Pat. No. 710,357 or Hitchcock, U.S. Pat. No. 789,911; or according to the teachings of Pilkington, U.S. Pat. Nos. 3,083,551 and 3,220,816; or according to the teachings of Edge and Kunkle, application Ser. No. 338,497 filed Mar. 6, 1973 now U.S. Pat. No. 3,843,346. These patents describe processes in which continuous sheets of flat glass are formed while the glass being formed is supported on molten metal. These patents are primarily concerned with different methods for delivering molten glass to the surface of a pool of molten metal and different methods of treating the glass while supported thereon. After a continuous sheet of glass has been formed, it has been shown to be removed from the surface of a pool of supporting molten metal by lifting it slightly and conveying it away from the pool of molten metal. It has also been shown in U.S. Pat. No. 3,233,995 to Javaux and U.S. Pat. No. 3,420,647 to Charnock that molten glass delivered onto the supporting surface of a pool of molten metal may be cooled insufficiently to form a continuous sheet of glass having fixed dimensions and then the unfinished layer of glass is drawn upwardly from the surface of a pool of molten metal to form a continuous sheet of glass having stable dimensions. The layer of glass is cooled and formed during such upward drawing, with such drawing being in the nature of sheet glass drawing as known per se in the Pittsburgh, Colburn or Fourcault process.
In the cross-referenced, related application already referred to, Kunkle describes a process wherein a layer of molten glass is delivered onto a surface of a pool of molten metal and is advanced thereon and cooled to form a dimensionally stable, continuous sheet of glass having a fixed width and thickness, and this completely formed sheet of glass is then lifted upwardly from the surface of the pool of molten metal and conveyed upwardly, preferably vertically, from the pool of molten metal. As the ascending sheet of glass is conveyed upwardly, it is engaged above the surface of the pool of molten metal by traction-applying means such as the rolls of a conveyor. It is desirable that stresses within the glass be avoided in the method of Kunkle as it is a method having the purpose of minimizing thermally-induced stresses within the glass during its horizontal advance, during its lifting and during its upward conveyance into and through the upward conveying apparatus provided. The present invention is concerned with means for alleviating and preventing the development of stresses within the glass due to misalignment or disorientation of the sheet of glass caused by uneven mechanical forces acting upon the sheet of glass as it enters a conveying mechanism. This invention provides for preventing substantial disorientation of a sheet of glass ascending upwardly from a pool of molten metal and entering the lowermost traction-applying engaging elements of a conveying apparatus.